Microbial calcification has proven to be a useful model for studying biologic mineral formation. The mineral species formed by Bacterionema matruchotii is crystallographically indistinguishable from biologic apatite of bones and teeth. The calcification nucleator of B. matruchotii has been identified as proteolipid: basic, hydrophobic protein complexed with acidic phospholipid. Calcifiable proteolipid has been isolated from marmoset bone and human dental calculus. A within-strain comparison of B. matruchotii and a variant exhibiting impaired calcifiability has provided insight into cellular regulation of calcification. A record of the process of mineral formation in the organism provides a baseline for further studies. The purpose of the proposed research is to define the mechanism of intracellular apatite deposition in B. matruchotii through continued characterization of the nucleating entity, metabolic studies and examination of the process of apatite formation. Cellular regulation of calcification will be investigated by examining the interaction of calcifiable proteolipid with cell membrane components and through comparative studies with other microorganisms. Methodology developed for the microbial system can then be applied to vertebrate mineral formation.